It may be possible to locate or track a person associated with a specific device indoors via a radio frequency (RE)-based tracking. Tracking people indoors on the basis of variations in the Earth's indoor magnetic field has also been proposed. This type of location discovery typically applies magnetic field strengths measured by a magnetometer carried by the person. The measured strength is compared to an existing indoor magnetic field map to derive the location of the magnetometer, and thus, the person.
However, the above techniques for detecting persons' movements require knowledge of an indoor map, such as the indoor magnetic field map. This drawback limits the application of these techniques only to certain buildings. In a building for which such indoor map is not available, these techniques may not be directly applied for acquiring knowledge of the persons' movements. Nevertheless, it may be of importance to detect movements at least on some level in any building, regardless of whether or not a map is available for the building.